Machine for inspecting glass containers

ABSTRACT

A machine for inspecting the finish of a glass container rotating at an inspection station. A pair of light sources have horizontal light axes which are orthogonally related and intersect the container axis. The light sources illuminate the container finish. The illuminated checks are seen by a camera which has a camera axis coincident with the container axis and intersects the light axes making an angle of 45 degrees with both light axes and the horizontal.

The present invention relates to machines, which inspect glasscontainers for defects, and more particularly, to a system whichinspects for cracks in translucent glass containers.

BACKGROUND OF THE INVENTION

In the glass container industry, small cracks or fracture in the glassare referred to as “check defects”. Checks can range from submillimeters to several hundred millimeters and can be oriented at anydirection from vertical to horizontal. Glass is not a crystallinestructure by nature, but most cracks propagate roughly along a plane ofsome orientation in space mostly determined by the shape of the glass atthat location. For example, a crack that began as a vertical crack atthe upper surface of the mouth primarily propagates in a vertical plane.Checks can appear in any orientation and on any portion of a containerand can exist wholly within the glass or may penetrate to one or bothsurfaces. Checks are considered phase objects and do not absorb lightlike a solid objects does. Checks are primarily reflective in nature iftheir opposed surface separation is at least half a wavelength of light.However, very few checks with a smaller separation will reflect lightand accordingly they will not likely be detectable by direct reflectionmethods, but they might have scattering points when they penetrate tothe one or both surfaces of the container and will scatter light back tothe sensors.

Most of these crack defects will drastically weaken the bottle, oftencausing it to rupture or to leak. Therefore, bottle manufactures like toremove these containers before they reach filing plants. Checksappearing near the mouth of the containers are called finish checks. Inthe glass bottle industry, the term “container finish” refers to theportion of the bottle that defines the mouth, threads or beads, and thering. The upper surface of the mouth is referred as the sealing surface.

Almost all commercially available check detectors work on the principleof reflected light. A conventional check detector consists of a seriesof continuously operating light spot light sources and associatedphotodetectors that are positioned so that known checks on a bottlerotating at an inspection station will reflect light from one of thesources to one of the photo-detectors. Signal processing of thephotodetector outputs recovers the sharp peaks while rejecting lowerfrequency signal variations caused by ambient light, reflection from thebottle sidewall, etc.

While commercially available check detectors are successfully deployedon most glass bottle production lines, there are several drawbacks tothe approach. A few of those are: many point sensors are required formany possible reflection angles; some sensor angles are difficult toposition; additional sensors and lights need to be added as moreproduction defects appear; time consuming setup is required for eachtype of container; and the difficulty of reproducing the same setup fromone inspection line to another.

The following U.S. Pat. Nos. 4,701,612, 4,945,228, 4,958,223, 5,020,908,5,200,801, 5,895,911, 6,104,482, 6,211,952, and 6,275,287 all relate todevices that detect defects in the finish of a container.

OBJECT OF THE INVENTION

It is an object of the present invention to provide an apparatus forinspecting glass containers, which can detect vertical, horizontal, andany other angle cracks on a bottle which is user friendly and easilyadjusted. Another object of this invention is to provide a detector thatcan detect known types of checks and also any new checks withoutspecific setup requirements.

Other objects and advantages of the present portion of this inventionwill become apparent from the following accompanying drawings whichillustrate, in accordance with the mandate of the patent statutes, apresently preferred embodiment incorporating the principles of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become apparent from the following accompanyingdrawings which illustrate, in accordance with the mandate of the patentstatutes, a presently preferred embodiment.

FIG. 1 is an oblique elevational schematic view of an inspection stationof a machine for inspecting glass containers for checks and otherdefects, made in accordance with the teachings of the present invention.

FIG. 2 is a block diagram showing the operation of the pairs of lightsources and camera shown in FIG. 1;

FIG. 3 is a schematic top view of the container at the inspectionstation showing the light axes of a pair of light sources and thecamera.

FIG. 4 is a schematic elevational view showing the light axes of thelight sources and camera shown in FIG. 3.

FIG. 5 is a logic diagram illustrating the operation of the camerasystem of the inspection machine;

FIG. 6 is a logic diagram illustrating the operation of the lightingsystem of the inspection machine;

FIG. 7 is a timing diagram illustrating the operation of the lightsources;

FIG. 8 is a side elevational view of one of the light sources; and

FIG. 9 is an elevational view showing how the LED's of one of the lightsources are aimed toward the finish.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In a machine for inspecting glass containers (bottles), the containers10 are transported along a conveyor 12 to an inspection stationillustrated in FIG. 1. The conveyor may be a linear belt or a turrettype feed system. A container 10 is engaged by upper and lower rearpairs of idler rollers 14 and a front drive wheel 16 so that rotation ofthe drive wheel in the clockwise direction will rotate the container inthe counterclockwise direction. There is conveyor dwell of sufficientduration at the inspection machine so that the container can be rotatedmore than 360 degrees while the inspection takes place. A containerpresent sensor 18 will sense the presence of a container at theinspection station (the sensor can be upstream and the actual presenceof the container at the inspection station could be defined by anencoder count following the sensing of the container by the upstreampart present sensor. Light sources (Light Source #1/20 (see FIGS. 1 and2) and Light Source #2/21) illuminate the finish portion of thecontainer and a Camera/22 images the finish portion.

FIG. 2 illustrates the operation of the Camera and Light Sources. AComputer 24 delivers On/Off signals to Light Source #1/20 and LightSource #2/21 and delivers Camera Trigger signals to the Camera/22. TheCamera has a matrix array of elements (pixels) to receive an image ofthe finish portion of the container during the Camera's exposure period.The Camera could be a CCD, MOS or like camera which will store an imageuntil the next Trigger Signal. When a Trigger Signal is received, theexisting image will be captured and transferred, as an “Acquisition”, tothe Computer so that it can be recorded and processed by the Computer.The Computer will issue a Reject Signal if a defect is identified.

As can be seen from FIGS. 3 and 4, the Light Axis for each light source,which is in the positive “Z” plane of the container, is horizontal andintersects the axis “A” of the container. The two light axes areorthogonal to each other and 450 to a vertical plane including theCamera Detector Axis. The Detector Axis for the Camera/22, which islocated in the negative “Z” plane, is approximately 45° from horizontal.With this relationship, the camera is looking at a dark field and seeingonly light coming from the checks. The light sources and camera aresupported by structure 28 that can be vertically displaced andhorizontally displaced to reposition the system for differentheight/diameter containers.

To start an inspection, the machine will Transfer A Bottle To TheInspection Station/30. Following a time sufficient for the rotation ofthe bottle, by the drive wheel, to become stable, the Computer willTrigger The Camera/32. This starts the acquisition of the image. Thefollowing explanation is provided in terms of angles for purposes ofclarity, but it should be understood that in a digitally controlledcamera, instructions may be time based rather than defining actualangles so that when something is to occur in an approximate θ° (60°angle in the preferred embodiment), an approximate time (number ofpulses) may be selected which approximately corresponds to that angleand where events are desired approximately every 7.5°, for example, thepulses could be divided by 8. When the query “Has Bottle Rotated θ°?”/34(θ° or a selected number of pulses corresponding approximately to thatangle of rotation can be set) is answered in the affirmative, theComputer will Transfer And Record The Acquisition/36. Once the Camera istriggered, the Camera will capture data until the Camera is againtriggered (following the rotation through θ°). When the Computer answersthe query “Y Acquisitions?” in the negative, the Computer will againTrigger The Camera/32. When the computer answers the query “YAcquisitions?”/38 in the affirmative (“Y” may be set and is six in thepreferred embodiment), the Computer will Create An Image From YAcquisitions To be Analyzed/40. The image created (a Critical Addition),where as in the preferred embodiment “Y” is six, will represent theentire (approximately) 360° surface of the finish and will be theCritical Addition of six acquisitions each imaging eight illuminations.

The critical addition will be made in a manner that will maximize thedata that indicates that a defect is present. The Critical Addition canrepresent for each pixel location, the highest intensity of thecorresponding pixel in all six Acquisitions which will make up theCritical Addition. Then, when the Computer answers the inquiry NextBottle?/44 in the affirmative, the next bottle can be processed.

An image processing technique may be used to enhance the signal createdby checks from signal created by mold features of the container. First,a reference or “mask image”, can be created using a set of samplecontainers without defects running through the inspection setup(containers without defects are referred as “good ware” and containerswith defects that need to be removed during the inspection as “badware”). To incorporate all the signals created by good ware fromdifferent molds that may contain slightly different structuralvariations, and small variations of signals due to vibrations androtation, a large number of images can be acquired and processed tocreate the mask image. These images contain almost all the possiblevariation of light reflection by mold marks, threads, seams, and curvedsurface of good ware. Mask image is created by combining the all thegood ware images. A mask image is created and is compared with thereference mask created with good ware. The difference between the imageand the mask shows the signals created by check defects.

FIG. 6 illustrates the operation of the light sources. When the Computeranswers the query “Is Image Acquisition To Begin?”/52 in theaffirmative, the Computer will Turn Lights “On” For Angle “α”/54 (“α”may be set and could be a defined number of pulses). When the Computeranswers the query “Has Container Rotated “φ°”/56 in the affirmative (φcan be set), and answers the query “Has Container Rotated θ°?”/58 in thenegative, the light sources will again be turned “on”. When this inquiryis answered in the affirmative (θ/φ pulse per acquisition), and thequery Have “Y” Images Been Acquired?/60”, in the negative the entiresurface has not been imaged and the entire process can be repeated until“Y” images have been acquired (Y pulses per acquisition). Then, when thecomputer answers the inquiry “Has Next Container Been Sensed?”/62 in theaffirmative, the entire process can be repeated for the next bottle. Ifthe lights are to be on for the entire time that the camera is triggered(α can be set to equal θ°).

To reduce noise, α is, in the preferred embodiment, defined so that thesurface will be illuminated a small portion (25%) of the angle θ°.Checks that will cause a container to be rejected have been found to beimaged when the light sources are “on” only a small fraction of α. Thisfraction can be empirically varied to achieve a desired result. Whilethe imaging process has been disclosed with reference to checks in thefinish area of the container, it can be used to identify body or heelchecks and other defects.

FIG. 7 is a timing diagram for an Acquisition comprised of light sourcesturned on α degrees for every φ° (7.5° in the preferred embodiment)through θ° (60° in the preferred embodiment). The lower the ratio ofα/φ°, the less noise will be available to interfere with the desiredsignal.

The light sources 70 (FIGS. 8 and 9) are mirror images and are segmentsof an arc. As shown the light source, mounted on a flat panel 71, isperpendicular to the Light Axis and faces the finish of the container 10which is shown in dotted lines. The segment has inner and outer (orthree or four, . . . ) rows of LED's 72 with the central LED's 74, whichdefine the Light Axis, standing parallel to the Light Axis and with theremaining LED's being progressively tilted toward the light axis as theyproceed away from the Light Axis. The preferred location of the LightAxis is at the sealing surface 74 but it can be located from the sealingsurface to the bottom of the finish. The ideal geometry that thepreferred embodiment attempts to approach is that of conicalillumination, where the top and bottom of the cone are dark so that thecamera will not see any direct reflections of light. Viewing the finishas a torus, this conical geometry allows the maximum light to beprojected onto the finish with direct reflection. Only an anomaly in thefinish (a check) will generate direct reflections to the camera.

This apparatus has following advantages: because the area sensor imagean area of the bottle, it is possible to detect almost all the checks inthat region. This make the inspection is independent of the specificorientation and location of the check, and thus enable detecting “new”checks without changing the setup. The positioning of the area arraysensors and light sources would not depend essentially on the geometryof the bottle. It will be easier to setup for most of the containerswith little or no adjustments.

1. A machine for inspecting the finish area of a vertical glasscontainer at an inspection station comprising means for rotating theglass container at the inspection station, first and second verticallyextending light sources, the light axis of each of said first and secondlight sources being horizontal and defining together an orthogonal angleat the axis of the container at the finish and, a camera having adetector axis intersecting said container axis with said light axes anddefining an angle of approximately 45 degrees above the horizontal and45 degrees with each light axis.
 2. A machine for inspecting the finisharea of a glass container at an inspection station according to claim 1,wherein said first light source is a vertical array of LED's includingat least one LED defining the first light source light axis and whereinsaid second light source is a vertical array of LED's including at leastone LED defining the second light source light axis.
 3. A machine forinspecting the finish area of a glass container at an inspection stationaccording to claim 2, wherein each light source includes a firstplurality of LED's extending vertically above the LED defining the lightaxis for that light source and a second plurality of LED's extendingvertically below the LED defining the light axis for that light source.4. A machine for inspecting the finish area of a glass container at aninspection station according to claim 3, wherein each of said firstplurality of LED's is progressively tilted toward the first light sourcelight axis as a function of distance from the first light axis andwherein each of said second plurality of LED's is progressively tiltedtoward the second light source light axis as a function of the distancefrom the second light axis.
 5. A machine for inspecting the finish areaof a glass container at an inspection station according to claim 2,wherein the vertical array of LED's includes horizontally adjacent pairsof LED's.
 6. A machine for inspecting the finish area of a glasscontainer at an inspection station according to claim 2, wherein saidvertical arrays of LED's form mirrored arcs.
 7. A machine for inspectingthe finish area of a glass container at an inspection station accordingto claim 4, wherein said vertical arrays of LED's form mirrored arcs. 8.A machine for inspecting the finish area of a glass container at aninspection station according to claim 5, wherein said vertical arrays ofLED's form mirrored arcs.